This application claims priority under 35 USC 119 of Japanese patent application Ser. No. 2000-171176 filed on Jun. 7, 2000, the entire disclosure of which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to a fuel injection control apparatus of an engine for correcting amounts of fuel to be injected into respective cylinders of the engine in accordance with engine revolution speed variations between the engine cylinders, which likely occur when the engine is operated in a low speed and light load condition.
2. Description of the Related Art
In general, an engine such as a diesel engine having a plurality of cylinders has manufacturing errors or tolerances in various parts used to build injectors or other parts. In addition, the engine cylinders experience aging. Consequently, the cylinders have different combustion conditions such as different combustion periods and heat generation. As a result, combustions take place in different manners in the cylinders, and therefore the cylinders exert different engine revolution speeds the moment the combustions occur in the cylinders. This occasionally causes engine vibrations which are significant when the engine is operating at a slow speed with a light load.
In order to suppress the engine revolution speed variations between the cylinders, Japanese Patent Application, Laid Open Publication Nos. 61-46444 and 3-100351 proposed measures for amending amounts of fuel to be injected into the respective cylinders. A fuel injection control apparatus disclosed in Japanese Patent Application Laid-Open Publication No. 61-46444 detects engine revolution speeds of the respective cylinders at predetermined crankshaft angles before and after combustion during stable idling, and then adjusts the amounts of fuel injection such that the cylinders have the same revolution speed discrepancy. When the engine is operated outside the idling range, the above adjustment is further adjusted in response to the engine running condition. Accordingly, a driver can experience a smooth driving without engine revolution speed variations regardless of the engine revolution speed and engine load.
Japanese Patent Application Laid-Open Publication 3-100351, which claims priority of DE P 3929746.2 filed Sep. 7, 1989, discloses a fuel injection control apparatus that has a correction means for correcting a fuel feed signal at predetermined intervals when an engine is operated in a stable condition with respect to an exhaust gas temperature, engine revolution speed, engine torque and other aspects at the final stage of the engine manufacturing process. Values detected by sensors are used by a calculation circuit to decide a correction value. This correction value is stored in the form of a map inside a memory in connection with various engine revolution speeds and loads even after the engine is deactivated. This value is utilized again to adjust the deviations in the fuel injection between the cylinders when the engine is restarted.
The engine revolution speed variations cause the engine vibrations when the engine is operated in a low speed-light load condition. Therefore, the above described engine fuel injection adjustment is generally applied to the cylinders when the engine is operated under such a condition. If a considerable change occurs in the engine revolution speed and load, e.g., when the engine running condition switches from the idling to the non-idling condition or vice versa, a steep change is caused in the amount of fuel injection upon changing of the engine running condition because of cancellation or application of the fuel adjustment. This produces impulsive vibrations in the engine, which are in turn transmitted to a driver and passengers in a vehicle as well as a vehicle body.
An object of the present invention is to overcome the above described problems.
According to one aspect of the present invention, there is provided a fuel injection control apparatus of an engine having a plurality of cylinders including a basic injection calculation means for calculating a basic amount of fuel to be injected into the cylinders in accordance with an engine running condition, an adjustment deciding means for deciding an amount of adjustment ultimately made to the basic amount of fuel on the basis of an engine revolution speed difference detected between the cylinders, an adjustment necessity determination means for determining whether the fuel adjustment is needed or not on the basis of the engine running condition, and a final injection deciding means for deciding a total amount of fuel to be injected into the cylinders on the basis of the basic amount of fuel and the amount of adjustment when the adjustment necessity determination means changes its determination, with the adjustment being made in a stepwise manner such that a steep change does not occur in the total amount of fuel.
The basic fuel calculation means first calculates the basic amount of fuel to be injected based on the engine operating condition. Then, the engine revolution speed difference between the cylinders is detected. In order to cancel this engine revolution speed difference, the adjustment deciding means decides the ultimate amount of adjustment (i.e., total amount of adjustment). In the present invention, this adjustment is not applied to the basic amount of fuel immediately. Before the adjustment is made, the adjustment necessity determination means determines whether the adjustment is needed based on the engine operating condition. When the determination means changes its determination (from yes (xe2x80x9cneededxe2x80x9d) to no (xe2x80x9cnot neededxe2x80x9d) or vice versa), the final injection deciding means prepares the stepwise decreasing or increasing scheme applied to the total amount of adjustment. The final injection deciding means then adjusts the total amount of injection based on the basic amount of injection and the stepwise changing amount of adjustment.
When the determination of the adjustment necessity determination means switches from xe2x80x9cneededxe2x80x9d to xe2x80x9cnot neededxe2x80x9d or vice versa, the amount of adjustment will not be immediately canceled from or added to the basic amount of fuel. Rather, the amount of adjustment is stepwise decreased or increased. Accordingly, the total amount of fuel injection changes gradually. As a result, the combustion condition does not change suddenly, and the engine vibrations do not occur.
When the determination of the adjustment necessity determination means switches from xe2x80x9cnot neededxe2x80x9d to xe2x80x9cneededxe2x80x9d, the final injection deciding means multiplies the difference between the total (or ultimate) adjustment and a previous stepwise adjustment by a predetermined coefficient (less than one), and adds the resulting value to the previous stepwise adjustment to decide the stepwise adjustment of this time. The final injection deciding means then adds this stepwise adjustment to the basic fuel to obtain the total fuel injection of this time. The final injection deciding means does not add the ultimate adjustment to the basic fuel upon determining that the adjustment is needed. If the ultimate adjustment were immediately applied, the total amount of fuel injection would rise steeply. In the present invention, the adjustment gradually increases (or approaches) step by step to the ultimate value.
When the absolute value of the difference between the ultimate amount of adjustment and the previous stepwise amount of adjustment becomes less than a prescribed value, the final injection deciding means adds the ultimate amount of adjustment to the basic amount of injection and uses the resulting value as the total amount of injection of this time. If the absolute value of the difference between the ultimate amount of adjustment and the previous stepwise amount of adjustment is smaller than the prescribed value, the stepwise adjustment is no longer necessary.
When the determination of the adjustment necessity determination means switches from xe2x80x9cneededxe2x80x9d to xe2x80x9cnot neededxe2x80x9d, on the other hand, the final injection deciding means multiplies the difference between zero and a previous stepwise adjustment by a predetermined coefficient (less than one), and adds the resulting value (this value is a negative value) to the previous stepwise adjustment to decide the stepwise adjustment of this time. The final injection deciding means then adds this stepwise adjustment to the basic fuel to obtain the total fuel injection of this time. The final injection deciding means does not subtract the full amount of adjustment from the previous total amount of injection upon determining that the adjustment is not needed. If it occurred, the total amount of fuel injection would drop steeply. In the present invention, the adjustment gradually decreases to zero; the total amount of injection gradually approaches the basic amount of injection.
When the absolute value of the step wise adjustment becomes less than a prescribed value, the final injection deciding means employs the basic amount of injection as the total amount of injection of this time. If the stepwise adjustment is sufficiently small, it is no longer necessary.
Additional objects, benefits and advantages of the present invention will become apparent to those skilled in the art to which this invention relates from the subsequent description of the embodiments and the appended claims, taken in conjunction with the accompanying drawings.